Copied from stockholm krebs/3modules/reaktor2.nix (cc283503). The bot
itself goes to pkgs/reaktor2 (with blessings, which nixpkgs lacks),
since stockholm's packages output does not include it.

Copied from stockholm krebs/3modules/htgen.nix (cc283503), so it no
longer needs pkgs.htgen from the stockholm overlay.

barnacle's hosts block only had kartei.extraHosts, so starkstrom.r and
acheron.r did not resolve there. self.retiolum now exposes extraHosts
(v4v6/v6only) rendered like kartei's, and barnacle appends it.

deploy now always takes a machine and a target host. It extracts the
bulk key once, runs clan vars generate, copies the flake source to
/var/lib/deploy/incoming over ssh, builds it there in the transient unit
deploy-build (progress via nom), shows the source diff against the
running system's source and the closure diff, asks, uploads secrets and
switches in deploy-switch. Both units survive the ssh connection dying;
rerunning deploy attaches to a running one.

Render /etc/hosts, ssh known_hosts and ssh ports from kartei (plus the
superconfig-only cards in retiolum/) instead of stockholm's krebs.hosts,
and drop krebs.build.host everywhere: readers now use kartei.hosts or
networking.hostName, which comes from the clan machine name.

- remove stockholm users/hosts/build/dns/ssh imports; declare krebs.users
locally
- drop the acheron/starkstrom krebs.hosts cards; both now appear in every
machine's /etc/hosts
- neoprism: stop serving /hosts and /retiolum.hosts
- ignavia: move the styx tinc Address override onto the kartei-built host
file; the krebs.hosts one had no effect since the kartei cutover